U.S. patent application number 13/062488 was filed with the patent office on 2011-07-14 for electrode active material, method for producing same, electrode for nonaqueous secondary battery, and nonaqueous secondary battery.
Invention is credited to Atsushi Hatakeyama, Mitsuhiro Kishimi, Satoshi Kono.
Application Number | 20110171529 13/062488 |
Document ID | / |
Family ID | 42936126 |
Filed Date | 2011-07-14 |
United States Patent
Application |
20110171529 |
Kind Code |
A1 |
Kono; Satoshi ; et
al. |
July 14, 2011 |
ELECTRODE ACTIVE MATERIAL, METHOD FOR PRODUCING SAME, ELECTRODE FOR
NONAQUEOUS SECONDARY BATTERY, AND NONAQUEOUS SECONDARY BATTERY
Abstract
An electrode active material includes particles of a
lithium-containing composite oxide represented by the general
compositional formula: Li.sub.1+xMO.sub.2, where
-0.15.ltoreq.x.ltoreq.0.15, and M represents an element group of
three or more elements including at least Ni, Co and Mn, wherein
the ratios of Ni, Co and Mn to the total elements constituting M
satisfy 45.ltoreq.a.ltoreq.90, 5.ltoreq.b.ltoreq.30,
5.ltoreq.c.ltoreq.30 and 10.ltoreq.b+c.ltoreq.55, where the ratios
of Ni, Co and Mn are represented by a, b and c, respectively, in
units of mol %, the average valence A of Ni in the whole particles
is 2.2 to 3.2, the valence B of Ni on the surface of the particles
has the relationship: B<A, the average valence C of Co in the
whole particles is 2.5 to 3.2, the valence D of Co on the surface
of the particles has the relationship: D<C, and the average
valence of Mn in the whole particles is 3.5 to 4.2.
Inventors: |
Kono; Satoshi; (Osaka,
JP) ; Kishimi; Mitsuhiro; (Osaka, JP) ;
Hatakeyama; Atsushi; (Osaka, JP) |
Family ID: |
42936126 |
Appl. No.: |
13/062488 |
Filed: |
March 10, 2010 |
PCT Filed: |
March 10, 2010 |
PCT NO: |
PCT/JP2010/053969 |
371 Date: |
March 4, 2011 |
Current U.S.
Class: |
429/223 ;
252/182.1; 429/224; 429/231.3 |
Current CPC
Class: |
C01P 2004/32 20130101;
H01M 4/485 20130101; H01M 4/621 20130101; H01M 4/505 20130101; C01G
53/50 20130101; C01G 53/44 20130101; C01P 2002/54 20130101; Y02E
60/10 20130101; C01P 2002/52 20130101; H01M 4/525 20130101; C01P
2004/61 20130101; H01M 10/0525 20130101; H01M 4/626 20130101; C01P
2006/40 20130101; C01P 2006/12 20130101; H01M 4/131 20130101; H01M
4/625 20130101; H01M 4/1391 20130101; C01P 2006/11 20130101; H01M
4/0471 20130101 |
Class at
Publication: |
429/223 ;
252/182.1; 429/224; 429/231.3 |
International
Class: |
H01M 4/525 20100101
H01M004/525; H01M 4/88 20060101 H01M004/88; H01M 4/505 20100101
H01M004/505; H01M 4/131 20100101 H01M004/131 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2009 |
JP |
2009-095427 |
Feb 17, 2010 |
JP |
2010032831 |
Claims
1. An electrode active material comprising particles of a
lithium-containing composite oxide represented by the general
compositional formula: Li.sub.1+xMO.sub.2, where x is within a
range of -0.15.ltoreq.x.ltoreq.0.15, and M represents an element
group of three or more elements including at least Ni, Co and Mn,
wherein the ratios of Ni, Co and Mn to the total elements
constituting M satisfy 45.ltoreq.a.ltoreq.90, 5.ltoreq.b.ltoreq.30,
5.ltoreq.c.ltoreq.30 and 10.ltoreq.b+-c.ltoreq.55, where the ratios
of Ni, Co and Mn are represented by a, band c, respectively, in
units of mol %, the average valence A of Ni in the whole particles
is 2.2 to 3.2, the valence B of Ni on the surface of the particles
has the relationship: B<A, the average valence C of Co in the
whole particles is 2.5 to 3.2, the valence D of Co on the surface
of the particles has the relationship: D<C, and the average
valence of Mn in the whole particles is 3.5 to 4.2.
2. The electrode active material according to claim 1, wherein the
average valence A of Ni in the whole particles is 2.2 to 2.9, and
the valence B of Ni on the surface of the particles has the
relationship: B<A.
3. The electrode active material according to claim 1, wherein the
ratio b of Co and the ratio c of Mn have the relationship:
b>c.
4. The electrode active material according to claim 1, wherein the
ratio b of Co and the ratio c of Mn have the relationship:
b<c.
5. The electrode active material according to claim 1, wherein the
lithium-containing composite oxide is represented by the general
compositional formula:
Li.sub.1+xNi.sub.1-d-eCo.sub.dMn.sub.eO.sub.2, where
-0.15.ltoreq.x.ltoreq.0.15, 0.05.ltoreq.d.ltoreq.0.3,
0.05.ltoreq.e.ltoreq.0.3, and 0.1.ltoreq.d+e.ltoreq.0.55.
6. The electrode active material according to claim 1, wherein the
lithium-containing composite oxide is formed by washing a composite
oxide of Li and the element group M with water or an organic
solvent and heat treating the washed composite oxide at a
temperature of 600 to 1000.degree. C. in an atmosphere containing
18 vol % or more of oxygen.
7. The electrode active material according to claim 1, wherein the
particles of the lithium-containing composite oxide have a true
density of 4.55 to 4.95 g/cm.sup.3.
8. The electrode active material according to claim 1, wherein the
particles of the lithium-containing composite oxide have a tap
density of 2.4 to 3.8 g/cm.sup.3.
9. The electrode active material according to claim 1, wherein in
the particles of the lithium-containing composite oxide, the ratio
of primary particles having a particle size of 1 .mu.m or less to
the total primary particles of the lithium-containing composite
oxide particles is 30 vol % or less.
10. The electrode active material according to claim 1, wherein the
lithium-containing composite oxide has a BET specific surface area
of 0.1 to 0.3 m.sup.2/g.
11. The electrode active material according to claim 1, wherein the
particles of the lithium-containing composite oxide has a spherical
shape or a substantially spherical shape.
12. An electrode for a non-aqueous secondary battery comprising an
electrode material mixture layer containing the electrode active
material according to claim 1.
13. The electrode for a non-aqueous secondary battery according to
claim 12, wherein the electrode material mixture layer has a
density of 3.2 to 3.8 g/cm.sup.3.
14. A non-aqueous secondary battery comprising a positive
electrode, a negative electrode and a non-aqueous electrolyte,
wherein the positive electrode includes an electrode material
mixture layer containing the electrode active material according to
claim 1.
15. A method for producing an electrode active material including
particles of a lithium-containing composite oxide represented by
the general compositional formula: Li.sub.1+xMO.sub.2, where x is
within a range of -0.15.ltoreq.x.ltoreq.0.15, and M represents an
element group of three or more elements including at least Ni, Co
and Mn, in which the ratios of Ni, Co and Mn to the total elements
constituting M satisfy 45.ltoreq.a.ltoreq.90, 5.ltoreq.b.ltoreq.30,
5.ltoreq.c.ltoreq.30 and 10.ltoreq.b+c.ltoreq.55, where the ratios
of Ni, Co and Mn are represented by a, b and c, respectively, in
units of mol %, the average valence A of Ni in the whole particles
is 2.2 to 3.2, the valence B of Ni on the surface of the particles
has the relationship: B<A, the average valence C of Co in the
whole particles is 2.5 to 3.2, the valence D of Co on the surface
of the particles has the relationship: D<C, and the average
valence of Mn in the whole particles is 3.5 to 4.2, the method
comprising the steps of washing a composite oxide of Li and the
element group M with water or an organic solvent; and heat treating
the washed composite oxide at a temperature of 600 to 1000.degree.
C. in an atmosphere containing 18 vol % or more of oxygen.
16. The method for producing an electrode active material according
to claim 15, wherein the average valence A of Ni in the whole
particles is 2.2 to 2.9, and the valence B of Ni on the surface of
the particles has the relationship: B<A.
17. The method for producing an electrode active material according
to claim 15, wherein the heat treatment time in the heat treatment
step is 1 to 24 hours.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrode for a
non-aqueous secondary battery having a high capacity and excellent
thermal stability, an electrode active material for use in such an
electrode, a method for producing such an electrode active
material, and a non-aqueous secondary battery that includes such an
electrode and that has a high capacity, good safety even in high
temperature environments, and excellent charge/discharge cycle
characteristics and storage characteristics.
BACKGROUND ART
[0002] With the development of portable electronic devices such as
cell phones and notebook personal computers and the
commercialization of electric vehicles in recent years, demand is
increasing for small, lightweight and high capacity secondary
batteries and capacitors. Currently, high capacity secondary
batteries and capacitors that can fulfill the demand commonly
employ LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4 and the like as
positive electrode active materials.
[0003] However, these positive electrode active materials have the
following drawbacks. LiCoO.sub.2 has low thermal stability in the
charged state. LiNiO.sub.2 has a capacity higher than that of
LiCoO.sub.2, but is less thermally stable than LiCoO.sub.2 in the
charged state. Furthermore, LiMn.sub.2O.sub.4 has high thermal
stability in the charged state, but has a capacity per volume
smaller than that of LiCoO.sub.2.
[0004] Under the circumstances, in order to achieve both thermal
stability of LiMn.sub.2O.sub.4 and the high capacity of
LiNiO.sub.2, lithium-containing composite oxides have been proposed
that has the layered crystal structure of LiNiO.sub.2 and in which
a certain amount of Ni has been substituted by Mn having high
thermal stability (for example, Patent Documents 1 to 3).
[0005] In particular, Patent Document 3 discloses a method for
producing a lithium-containing composite oxide as described above
that includes a process in which raw material compounds are mixed
and baked, and thereafter the mixture is washed with water and
dried. According to Patent Document 3, the method removes
impurities and by-products attached to the baked product obtained
by baking the mixture of raw material compounds, thereby providing
a lithium-containing composite oxide having excellent thermal
stability.
Prior Art Documents
Patent Documents
[0006] Patent Document 1: JP 2003-221236 A
[0007] Patent Document 2: WO 02/40404A
[0008] Patent Document 3: JP 2007-273108 A
SUMMARY OF INVENTION
Problem to be Solved by the Invention
[0009] However, lithium-containing composite oxides as disclosed in
Patent Documents 1 to 3 have low initial charge/discharge
efficiency, and thus the capacity tends to decrease significantly.
Also, the lithium-containing composite oxides have a low true
density, and thus it is difficult to increase the capacity when
they are used in electrodes. That is, there is still some room for
improvement in terms of further increase in battery capacity, as
well as in terms of battery charge/discharge cycle characteristics
and storage characteristics.
[0010] The present invention has been conceived under the
above-described circumstances, and provides an electrode for a
non-aqueous secondary battery having a high capacity and high
thermal stability, an electrode active material that can constitute
such an electrode, a method for producing such an electrode active
material, and a non-aqueous secondary battery that includes such an
electrode and that has a high capacity, good safety even in high
temperature environments, as well as excellent charge/discharge
cycle characteristics and storage characteristics.
Means for Solving Problem
[0011] An electrode active material according to the present
invention is an electrode active material including particles of a
lithium-containing composite oxide represented by the general
compositional formula: Li.sub.1+xMO.sub.2, where x is within a
range of -0.15.ltoreq.x.ltoreq.0.15, and M represents an element
group of three or more elements including at least Ni, Co and Mn,
wherein the ratios of Ni, Co and Mn to the total elements
constituting M satisfy 45.ltoreq.a.ltoreq.90, 5.ltoreq.b.ltoreq.30,
5.ltoreq.c.ltoreq.30 and 10.ltoreq.b+c.ltoreq.55, where ratios of
Ni, Co and Mn are represented by a, b and c, respectively, in units
of mol %, the average valence A of Ni in the whole particles is 2.2
to 3.2, the valence B of Ni on the surface of the particles has the
relationship: B<A, the average valence C of Co in the whole
particles is 2.5 to 3.2, the valence D of Co on the surface of the
particles has the relationship: D<C, and the average valence of
Mn in the whole particles is 3.5 to 4.2.
[0012] An electrode for a non-aqueous secondary battery according
to the present invention includes an electrode material mixture
layer containing the electrode active material of the present
invention.
[0013] A non-aqueous secondary battery according to the present
invention is a non-aqueous secondary battery including a positive
electrode, a negative electrode and a non-aqueous electrolyte,
wherein the positive electrode includes an electrode material
mixture layer containing the electrode active material of the
present invention.
[0014] A method for producing an electrode active material
according to the present invention is a method for producing an
electrode active material including particles of a
lithium-containing composite oxide represented by the general
compositional formula: Li.sub.1+xMO.sub.2, where x is within a
range of -0.15.ltoreq.x.ltoreq.0.15, and M represents an element
group of three or more elements including at least Ni, Co and Mn,
in which the ratios of Ni, Co and Mn to the total elements
constituting M satisfy 45.ltoreq.a.ltoreq.90, 5.ltoreq.b.ltoreq.30,
5.ltoreq.c.ltoreq.30 and 10.ltoreq.b+c.ltoreq.55, where the ratios
of Ni, Co and Mn are represented by a, b and c, respectively, in
units of mol %, the average valence A of Ni in the whole particles
is 2.2 to 3.2, the valence B of Ni on the surface of the particles
has the relationship: B<A, the average valence C of Co in the
whole particles is 2.5 to 3.2, the valence D of Co on the surface
of the particles has the relationship: D<C, and the average
valence of Mn in the whole particles is 3.5 to 4.2, the method
including the steps of washing a composite oxide of Li and the
element group M with water or an organic solvent; and heat treating
the washed composite oxide at a temperature of 600 to 1000.degree.
C. in an atmosphere containing 18 vol % or more of oxygen.
Effects of the Invention
[0015] According to the present invention, it is possible to
provide an electrode for a non-aqueous secondary battery having a
high capacity and high thermal stability, an electrode active
material that can constitute such an electrode, a method for
producing such an electrode active material, and a non-aqueous
secondary battery that includes such an electrode and that has a
high capacity, good safety even in high temperature environments,
and excellent charge/discharge cycle characteristics and storage
characteristics.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1A is a plan view showing an example of a non-aqueous
secondary battery of the present invention, and FIG. 1B is a
cross-sectional view of FIG. 1A.
[0017] FIG. 2 is a perspective view of FIG. 1A.
MODES FOR CARRYING OUT THE INVENTION
[0018] An electrode active material according to the present
invention includes particles of a lithium-containing composite
oxide represented by the following general compositional formula
(1):
Li.sub.1+xiMO.sub.2 (1),
[0019] where x is within a range of -0.15.ltoreq.x.ltoreq.0.15, and
M represents an element group of three or more elements including
at least Ni, Co and Mn. The ratios of Ni, Co and Mn to the total
elements constituting M satisfy 45.ltoreq.a.ltoreq.90,
5.ltoreq.b.ltoreq.30, 5.ltoreq.c.ltoreq.30, and
10.ltoreq.b+c.ltoreq.55, where the ratios of Ni, Co and Mn are
represented by a, b and c, respectively, in units of mol %.
Furthermore, the average valence A of Ni in the whole particles is
2.2 to 3.2, the valence B of Ni on the surface of the particles has
the relationship ship: B<A, the average valence C of Co in the
whole particles is 2.5 to 3.2, the valence D of Co on the surface
of the particles has the relationship: D<C, and the average
valence of Mn in the whole particles is 3.5 to 4.2. The electrode
active material of the present invention is used as a positive
electrode active material for a non-aqueous secondary battery.
[0020] The lithium-containing composite oxide constituting the
electrode active material of the present invention contains an
element group M including at least Ni, Co and Mn. Ni is a component
that contributes to improving the capacity of the
lithium-containing composite oxide.
[0021] The ratio a of Ni is 45 mol % or more, and more preferably
50 mol % or more, based on the total number of elements of the
element group M in the general compositional formula (1),
representing the lithium-containing composite oxide, taken as 100
mol % from the viewpoint of achieving improved capacity of the
lithium-containing composite oxide. However, if the ratio of Ni in
the element group M is too large, for example, the amounts of Co
and Mn will be small, reducing the effects of these elements.
Accordingly, the ratio a of Ni is 90 mol % or less based on the
total number of elements of the element group M in the general
compositional formula (1), representing the lithium-containing
composite oxide, taken as 100 mol %.
[0022] The electrical conductivity of the lithium-containing
composite oxide decreases as the average valence of Ni in the whole
particles decreases. Accordingly, in the lithium-containing
composite oxide particles, the average valence A of Ni in the whole
particles measured by the method described below in the following
examples is 2.2 to 3.2, and more preferably 2.2 to 2.9. This
enables stable synthesis even in the atmospheric air, and it is
possible to obtain high capacity lithium-containing composite oxide
particles having excellent productivity and thermal stability.
[0023] Also, in the lithium-containing composite oxide particles,
the valence B of Ni on the surface of the particles measured by the
method described below in the following examples is smaller than
the average valence A of Ni in the whole particles, or in other
words, has the relationship: B<A. This makes Ni on the surface
of the particles inert and suppresses side reactions in the
battery, and it is therefore possible to obtain a battery having
excellent charge/discharge cycle characteristics and storage
characteristics.
[0024] The valence B of Ni on the surface of the particles need
only be smaller than the average valence A of Ni in the whole
particles, but the average valence A of Ni in the whole particles
can vary according to the ratio of Ni in the lithium-containing
composite oxide, and thus the preferable range of the valence B of
Ni on the surface of the particles varies as well according to the
ratio of Ni in the lithium-containing composite oxide. For this
reason, it is difficult to specify a preferred range of the valence
B of Ni on the surface of the particles, but for example, in the
lithium-containing composite oxide particles, the difference (A-B)
between the average valence A of Ni in the whole particles and the
valence B of Ni on the surface of the particles is preferably 0.05
or more, and more preferably 0.1 or more. It is thereby possible to
better ensure the above-described effects obtained by providing the
difference between the average valence A of Ni in the whole
particles and the valence B of Ni on the surface of the particles.
However, it is difficult to produce a lithium-containing composite
oxide with a large difference (A-B), and thus the (A-B) value is
preferably 0.5 or less, and more preferably 0.2 or less.
[0025] Co contributes to the capacity of the lithium-containing
composite oxide and acts to improve the packing density in the
electrode material mixture layer of the electrode having the
lithium-containing composite oxide particles, but it may cause
increased cost and reduced safety if the amount is too large.
Accordingly, the ratio b of Co is 5 mol % or more and 30 mol % or
less based on the total number of elements of the element group M
in the general compositional formula (1), representing the
lithium-containing composite oxide, taken as 100 mol %.
[0026] From the viewpoint of increasing the capacity of the
lithium-containing composite oxide, the average valence C of Co in
the whole particles of the lithium-containing composite oxide,
which is measured by the method described below in the following
examples, is 2.5 to 3.2.
[0027] In the lithium-containing composite oxide particles, the
valence D of Co on the surface of the particles, which is measured
by the method described below in the following examples, is smaller
than the average valence C of Co in the whole particles, or in
other words, has the relationship: D<C. As described above, when
the valence of Co on the surface of the particles is smaller than
the average valence of Co in the whole particles, Li sufficiently
diffuses on the surface of the particles, and thus good
electrochemical characteristics can be ensured, and a battery
having excellent battery characteristics can be obtained.
[0028] The valence D of Co on the surface of the particles need
only be smaller than the average valence C of Co in the whole
particles, but the average valence C of Co in the whole particles
can vary according to the ratio of Co in the lithium-containing
composite oxide, and thus the preferable range of the valence D of
Co on the surface of the particles varies as well according to the
ratio of Co in the lithium-containing composite oxide. For this
reason, it is difficult to specify a preferred range of the valence
D of Co on the surface of the particles, but for example, in the
lithium-containing composite oxide particles, the difference (C-D)
between the average valence C of Co in the whole particles and the
valence D of Co on the surface of the particles is preferably 0.05
or more, and more preferably 0.1 or more. It is thereby possible to
better ensure the above-described effects obtained by providing the
difference between the average valence C of Co in the whole
particles and the valence D of Co on the surface of the particles.
However, it is difficult to produce a lithium-containing composite
oxide with a large difference (C-D), and thus the (C-D) value is
preferably 0.5 or less, and more preferably 0.2 or less.
[0029] Also, in the lithium-containing composite oxide, the ratio c
of Mn is 5 mol % or more and 30 mol % or less based on the total
number of elements of the element group M in the general
compositional formula (1) taken as 100 mol %. By including Mn in
the above-described amount in the lithium-containing composite
oxide so as to have Mn necessarily present in a crystal lattice,
the thermal stability of the lithium-containing composite oxide
particles can be increased, and it is thereby possible to obtain an
even safer battery. In other words, in the crystal lattice, Mn
stabilizes the layer structure together with divalent Ni, improving
the thermal stability of the lithium-containing composite
oxide.
[0030] Furthermore, in the lithium-containing composite oxide,
inclusion of Co suppresses variations of Mn valence associated with
doping and dedoping of Li during battery charge/discharge and
stabilizes the average Mn valence at a value near 4, further
increasing reversibility in charge/discharge. Accordingly, by using
an electrode active material composed of such a lithium-containing
composite oxide, it is possible to obtain a battery having
excellent charge/discharge cycle characteristics.
[0031] The specific average valence of Mn in the whole particles of
the lithium-containing composite oxide, which is measured by the
method described below in the following examples, is 3.5 to 4.2 in
order to stabilize the layer structure together with divalent
Ni.
[0032] It is preferable that the valence of Mn on the surface of
the particles of the lithium-containing composite oxide is equal to
the average valence of Mn in the whole particles. This is because
in this case, leaching of Mn, which may occur when the valence of
Mn on the surface of the particles is low, can be well
suppressed.
[0033] In the lithium-containing composite oxide, from the
viewpoint of better ensuring the effects obtained by combined use
of Co and Mn, the sum (b+c) of the ratio b of Co and the ratio c of
Mn is 10 mol % or more and 55 mol % or less, and more preferably 50
mol % or less, based on the total number of elements of the element
group M in the general compositional formula (1) taken as 100 mol
%.
[0034] The element group M in the general compositional formula (1)
representing the lithium-containing composite oxide may include an
element other than Ni, Co and Mn, such as Ti, Cr, Fe, Cu, Zn, Al,
Ge, Sn, Mg, Ag, Ta, Nb, B, P, Zr, Ga, W, Mo, V, Ca, Sr or Ba.
Addition of an alkaline-earth metal selected from Ca, Sr and Ba,
for example, promotes the growth of primary particles and improves
the crystallinity of the lithium-containing composite oxide, and it
is therefore possible to reduce active sites, improve the stability
over time when used as a coating material, and suppress
irreversible reactions with the electrolyte. To this end, it is
particularly preferable to use Ba.
[0035] However, in order to obtain sufficient effects of the
present invention, the ratio of the element other than Ni, Co and
Mn is preferably 15 mol % or less, and more preferably 3 mol % or
less based on the total number of elements of the element group M
taken as 100 mol %. On the other hand, in order to easily obtain
the effects of the element other than Ni, Co and Mn, the ratio of
the element is preferably 0.1 mol % or more. The element other than
Ni, Co and Mn of the element group M may be uniformly distributed
in the lithium-containing composite oxide, or may be segregated to
the particle surface or the like.
[0036] In the general compositional formula (1) representing the
lithium-containing composite oxide, when the ratio b of Co and the
ratio c of Mn in the element group M satisfy the relationship:
b>c, the growth of the lithium-containing composite oxide
particles is promoted, the packing density of the particles when
used in an electrode material mixture layer is increased,
lithium-containing composite oxide particles having higher
reversibility can be obtained, and thereby a further increase in
the capacity of the battery using such an electrode is
expected.
[0037] On the other hand, in the general compositional formula (1)
representing the lithium-containing composite oxide, when the ratio
b of Co and the ratio c of Mn in the element group M satisfy the
relationship: b<c, a lithium-containing composite oxide having
higher thermal stability can be obtained, and a further increase in
the safety of the battery using such an electrode is expected.
[0038] The lithium-containing composite oxide particles having the
above-described composition have a true density as large as 4.55 to
4.95 g/cm.sup.3, and thus is a material having a high volume energy
density. This is presumably because the true density of the
lithium-containing composite oxide containing Mn within a
predetermined range changes significantly according to the
composition of the lithium-containing composite oxide, but when the
composition is within a narrow composition range as described
above, the structure is stabilized and uniformity is increased, and
thus the true density takes a large value close to, for example,
the true density of LiCoO.sub.2. The particles have a large true
density as described above, whereby the capacity of the
lithium-containing composite oxide per mass can be increased, and a
material having excellent reversibility can be obtained.
[0039] The lithium-containing composite oxide has a large true
density particularly when it has a composition close to the
stoichiometric ratio. Specifically, in the general compositional
formula (1), x preferably is within the range of
-0.15.ltoreq.x.ltoreq.0.15, and by adjusting the value of x within
this range, increased true density and reversibility can be
obtained. More preferably, x is -0.05 or more and 0.05 or less. In
this case, the lithium-containing composite oxide can have a true
density as high as 4.6 g/cm.sup.3 or more.
[0040] The lithium-containing composite oxide constituting the
electrode active material of the present invention is preferably a
composite oxide represented by the following general compositional
formula (2):
Li.sub.1+xNi.sub.1-d-eCo.sub.dMn.sub.eO.sub.2 (2),
[0041] where -0.15.ltoreq.x.ltoreq.0.15, 0.05.ltoreq.d.ltoreq.0.3,
0.05.ltoreq.e.ltoreq.0.3, and 0.1.ltoreq.d+e.ltoreq.0.55. It is
preferable that d+e is 0.5 or less.
[0042] In the lithium-containing composite oxide particles, it is
preferable that the ratio of primary particles having a particle
size of 1 .mu.m or less to the total primary particles of the
lithium-containing composite oxide particles is preferably 30 vol %
or less, and more preferably 15 vol % or less. The
lithium-containing composite oxide particles preferably has a BET
specific surface area of 0.3 m.sup.2/g or less, and more preferably
0.25 m.sup.2/g or less. When the lithium-containing composite oxide
particles have such a configuration, the surface activity of the
particles can be optimally suppressed, and when the particles are
used as a positive electrode active material in a battery, the
generation of gas can be suppressed, and particularly when the
battery has a prismatic outer case, deformation of the outer case
can be suppressed, further improving the storage properties and the
service life.
[0043] In other words, in the lithium-containing composite oxide
particles, if the ratio of primary particles having a particle size
of 1 .mu.m or less to the total primary particles is too large, or
if the BET specific surface area is too large, the reaction area
will be large, increasing the number of active sites, and thus
easily causing irreversible reactions with water in the atmospheric
air, with the binder used to form an electrode material mixture
layer using the lithium-containing composite oxide particles as an
active material, or with the non-aqueous electrolyte in the battery
having the electrode, as a result of which problems are likely to
occur such as the outer case being deformed due to gas generated
within the battery, and the composition (paste, slurry or the like)
containing a solvent used to form the electrode material mixture
layer being gelled.
[0044] The lithium-containing composite oxide particles may contain
no primary particles having a particle size of 1 .mu.m or less. In
other words, the ratio of primary particles having a particle size
of 1 .mu.m or less may be 0 vol %. The BET specific surface area of
the lithium-containing composite oxide particles is preferably 0.1
m.sup.2/g or more in order to prevent the reactivity from
decreasing more than necessary. Furthermore, the lithium-containing
composite oxide particles preferably have a number average particle
size of 5 to 25 .mu.m.
[0045] The ratio of primary particles having a particle size of 1
.mu.m or less contained in the lithium-containing composite oxide
particles, the number average particle size of the
lithium-containing composite oxide particles and the number average
particle size of another active material, which will be described
later, can be measured by using a laser diffraction/scattering
particle size distribution analyzer such as Microtrac HRA available
from Nikkiso Co. Ltd. The BET specific surface area of the
lithium-containing composite oxide particles is a specific surface
area of micropores and active material surface obtained by
measuring the surface area and performing calculation by the BET
method, which is a theory for multilayer adsorption. Specifically,
the BET specific surface area is a value obtained using a specific
surface area measuring apparatus that uses nitrogen adsorption
method (Macsorb HM model-1201 available from Mountech Co., Ltd.) as
a BET specific surface area.
[0046] From the viewpoint of increasing the density of the
electrode material mixture layer included in the electrode that
uses the lithium-containing composite oxide particles as an active
material to increase the electrode capacity and hence the battery
capacity, the lithium-containing composite oxide particles
preferably have a spherical shape or a substantially spherical
shape. With this configuration, in a pressing step when producing
an electrode, details of which will be described later, when the
lithium-containing composite oxide particles are moved by pressing
so as to increase the density of the electrode material mixture
layer, the particles are effortlessly moved and smoothly
reoriented. It is therefore possible to reduce the pressing load,
reducing damage to the current collector caused by pressing, thus
increasing the electrode productivity. The lithium-containing
composite oxide particles, when having a spherical shape or a
substantially spherical shape, can withstand a larger pressing
pressure, and thus the electrode material mixture layer can be made
highly dense.
[0047] Furthermore, from the viewpoint of increasing the electrode
material mixture layer filling ability of the lithium-containing
composite oxide particles in the electrode using the
lithium-containing composite oxide particles, the
lithium-containing composite oxide particles preferably have a tap
density of 2.4 g/cm.sup.3 or more, more preferably 2.8 g/cm.sup.3
or more, and also preferably 3.8 g/cm.sup.3 or less. In other
words, the filling ability of the lithium-containing composite
oxide in the electrode material mixture layer can be increased by
making particles having a high tap density and having no pores
inside the particles or having a small porosity with a surface area
ratio of micropores of 1 .mu.m or less of 10% or less, measured by
observing the particle's cross section.
[0048] The tap density of the lithium-containing composite oxide
particles is a value determined through the following measurement
using Powder Tester Model PT-S available from Hosokawa Micron
Corporation. Firstly, particles are filled and leveled off in a
100-cm.sup.3 measurement cup, and tapped for 180 seconds while
compensating for a volume loss as appropriate. After completion of
tapping, excess particles are leveled off with a blade, thereafter,
mass W (g) is measured and tap density is determined by the
following equation:
Tap density=W/100.
[0049] The electrode active material (lithium-containing composite
oxide particles) of the present invention is produced by a
production method of the present invention including the steps of
washing a composite oxide of Li and the element group M and heat
treating the washed composite oxide in an oxygen-containing
atmosphere. In other words, with the production method of the
present invention described below, it is possible to produce an
electrode active material of the present invention composed of
lithium-containing composite oxide particles having the
above-described composition and the valence of each element, and
the above-described true density and tap density, as well as
various factors (the ratio of primary particles having a particle
size of 1 .mu.m or less, the BET specific surface area, the number
average particle size, and the shape).
[0050] The technique in which a baked lithium-containing composite
oxide is washed and heat-treated (including drying) to remove
impurities and the like contained in the baked product so as to
improve the characteristics of the lithium-containing composite
oxide is conventionally known as disclosed in, for example, Patent
Document 3. However, with the production method of the present
invention, the final product of lithium-containing composite oxide
contains a relatively large amount of Mn, and the processing
conditions (heat treatment conditions in particular) are optimized,
as a result of which in addition to removing the impurities, the
valences of Ni and Co on the surface of the particles of the
lithium-containing composite oxide are controlled to be smaller
than the average valences thereof in the whole particles, enabling
the production of lithium-containing composite oxide particles
having high electrochemical characteristics and serving as an
active material capable of suppressing side reactions in the
battery.
[0051] The composite oxide of Li and the element group M that is
used to produce the lithium-containing composite oxide particles is
obtained by baking a raw material compound containing Li and the
element group M. It is very difficult to obtain a highly pure
composite oxide of Li and the element group M by simply mixing and
baking a Li-containing compound, a Ni-containing compound, a
Co-containing compound and a Ni-containing compound. This is
presumably because it is difficult to uniformly disperse Ni, Co and
Mn during synthesis reaction of the lithium-containing composite
oxide as they have a low diffusion speed in solid, making it
difficult to uniformly disperse Ni, Co and Mn in the produced
lithium-containing composite oxide.
[0052] To address this, when synthesizing the composite oxide of Li
and the element group M, it is preferable to employ a method in
which a composite compound containing at least Ni, Co and Mn as
constituent elements and a Li-containing compound are baked. With
this method, highly pure lithium-containing composite oxide
particles are synthesized relatively easily. Specifically, a
composite compound containing Ni, Co and Mn is synthesized first,
and the composite compound is baked together with a Li-containing
compound, thereby Ni, Co and Mn are uniformly distributed during
the oxide forming reaction, and a highly pure composite oxide of Li
and the element group M is synthesized.
[0053] The method for synthesizing a composite oxide of Li and the
element group M is not limited to the method described above, but
it is surmised that the physical properties of the final product of
lithium-containing composite oxide, or in other words, the
stability of the structure, the reversibility in charge/discharge,
the true density and the like, change significantly depending on
through which process the composite oxide was synthesized.
[0054] Examples of the composite compound containing at least Ni,
Co and Mn include a coprecipitated compound, a hydrothermally
synthesized compound and a mechanically synthesized compound that
contain at least Ni, Co and Mn, and a compound obtained by heat
treating any of these compounds, and it is preferable to use an
oxide or hydroxide of Ni, Co and Mn such as
Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O,
Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2, or
Ni.sub.0.6Co.sub.0.3Mn.sub.0.1(OH).sub.2.
[0055] In the case of producing a lithium-containing composite
oxide containing an element other than Ni, Co and Mn as a part of
the element group M (for example, at least one element selected
from the group consisting of Ti, Cr, Fe, Cu, Zn, Al, Ge, Sn, Mg,
Ag, Ta, Nb, B, P, Zr, Ga, W, Mo, V, Ca, Sr and Ba, which are
hereinafter collectively referred to as an "element M'"), the
lithium-containing composite oxide can be synthesized by mixing and
baking a composite compound containing at least Ni, Co and Mn, a
Li-containing compound and an element M'-containing compound, but
it is preferable to use a composite compound containing at least
Ni, Co, Mn and the element M' instead of the composite compound
containing at least Ni, Co and Mn and the element M'-containing
compound. The amount ratios of Ni, Co, Mn and M' in the composite
compound may be adjusted as appropriate according to the intended
composition of the lithium-containing composite oxide.
[0056] As the Li-containing compound that can be used to synthesize
the composite oxide of Li and the element group M, various lithium
salts can be used. Examples include lithium hydroxide monohydrate,
lithium nitrate, lithium carbonate, lithium acetate, lithium
bromide, lithium chloride, lithium citrate, lithium fluoride,
lithium iodide, lithium lactate, lithium oxalate, lithium
phosphate, lithium pyruvate, lithium sulfate, and lithium oxide.
Among them, it is preferable to use lithium hydroxide monohydrate
because it does not generate emissions that cause harm to the
environment such as carbon dioxide, nitrogen oxides or sulfur
oxides.
[0057] To synthesize the composite oxide of Li and the element
group M, firstly, a composite compound containing at least Ni, Co
and Mn (the composite compound may further contain the element M'),
a Li-containing compound and optionally an element M'-containing
compound are mixed at a ratio substantially equal to the intended
composition of the lithium-containing composite oxide. In order to
obtain the final product of lithium-containing composite oxide
particles having a composition close to the stoichiometric ratio,
it is preferable to adjust the mixing ratio of the Li-containing
compound to the other raw material compounds such that the amount
of Li contained in the Li-containing compound is in excess of the
total amount of the element group M. The obtained raw material
mixture is then baked at, for example, 800 to 1050.degree. C. for 1
to 24 hours, and thereby a composite oxide of Li and the element
group M can be obtained.
[0058] When baking the raw material mixture, it is preferable to,
rather than increasing the temperature to a certain temperature at
a time, temporarily heat the raw material mixture to a temperature
(for example, 250 to 850.degree. C.) lower than the baking
temperature, maintain the temperature for preheating, and then
increase the temperature to the baking temperature to proceed the
reaction. It is also preferable to maintain the oxygen
concentration in the baking environment at a constant level.
[0059] This is performed to increase the uniformity of the
generated composite oxide of Li and the element group M and to grow
the crystal of the produced composite oxide of Li and the element
group M in a stable manner by causing a composite compound
containing at least Ni, Co and Mn (the composite compound may
further contain the element M'), a Li-containing compound and
optionally an element M'-containing compound to react stepwise
because the composition can be easily transformed to a
non-stoichiometric composition in the production process of the
composite oxide of Li and the element group M due to trivalent Ni,
which is unstable. In other words, when the temperature is
increased to the baking temperature at a time, or when the oxygen
concentration in the baking atmosphere decreases in the course of
baking, the compositional uniformity is likely to be compromised:
for example, the composite compound containing at least Ni, Co and
Mn (the composite compound may further contain the element M'), the
Li-containing compound and optionally the element M'-containing
compound are likely to react non-uniformly, and the produced
composite oxide of Li and the element group M may easily release
Li.
[0060] There is no particular limitation on the preheating time,
but the preheating time is usually approximately 0.5 to 30
hours.
[0061] The atmosphere used to bake the raw material mixture can be
an oxygen-containing atmosphere (or in other words, in the
atmospheric air), a mixed atmosphere of an inert gas (argon,
helium, nitrogen or the like) and an oxygen gas, an oxygen gas
atmosphere, or the like. In this case, the oxygen concentration is
preferably 15 vol % or more, and more preferably 18 vol % or more.
However, from the viewpoint of increasing the productivity of the
particles and hence the productivity of the electrode while
reducing the production cost of the lithium-containing composite
oxide particles, the raw material mixture is preferably baked in an
atmospheric air flow.
[0062] The gas flow rate used to bake the raw material mixture is
preferably 2 dm.sup.3/min or more per 100 g of the mixture. If the
gas flow rate is too low, or in other words, if the gas flow speed
is too slow, the compositional uniformity of the composite oxide of
Li and the element group M may be compromised. The gas flow rate
used to bake the raw material mixture is preferably 5 dm.sup.3/min
or less per 100 g of the mixture.
[0063] In the step of baking the raw material mixture, a dry-mixed
mixture may be used, but it is preferable to use a mixture obtained
by dispersing the raw material mixture in a solvent such as ethanol
to prepare a slurry, mixing the slurry with a planetary ball mill
or the like for approximately 30 to 60 minutes, and drying the
slurry. With this method, the uniformity of the synthesized
composite oxide of Li and the element group M can be further
increased.
[0064] Next, the obtained composite oxide of Li and the element
group M is washed. This washing step removes impurities and
by-products contained in the composite oxide of Li and the element
group M. Water or an organic solvent can be used to wash the
composite oxide of Li and the element group M. Examples of the
organic solvent include alcohols such as methanol, ethanol,
isopropanol and ethylene glycol; ketones such as acetone and methyl
ethyl ketone; ethers such as diethyl ether, ethyl propyl ether,
diisopropylether, dimethoxyethane, diethoxyethane,
trimethoxymethane, tetrahydrofuran, 2-methyltetrahydrofuran,
tetrahydrofuran derivatives, .gamma.-butyrolactone, dioxolane,
dioxolane derivatives and 3-methyl-2-oxazolidinone; esters such as
methyl formate, ethyl formate, methyl acetate, ethyl acetate and
phosphoric triester; and aprotic organic solvents such as
N-methyl-2-pyrrolidone (NMP), ethylene carbonate (EC), propylene
carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC),
diethyl carbonate (DEC), methyl ethyl carbonate (MEC), propylene
carbonate derivatives, dimethyl sulfoxide, formamide,
dimethylformamide, acetonitrile, nitromethane, sulfolane and
1,3-propane sultone. It is also possible to use an aminimide-based
organic solvent, a sulfur-containing organic solvent, a
fluorine-containing organic solvent, and the like. Water and the
organic solvents listed above may be used alone or in a combination
of two or more.
[0065] Furthermore, water and the organic solvent used for washing
may contain an additive, examples of which include celluloses such
as carboxymethyl cellulose, carboxy methyl ethyl cellulose, methyl
cellulose, ethyl cellulose and hydroxypropyl cellulose; saccharides
or oligomers thereof polyacrylic acid-based resins such as
polyacrylic acid, polyacrylic acid derivatives (sodium polyacrylate
and the like) and acrylic acid-maleic acid copolymer sodium;
polyacrylic acid-based rubbers such as polyacrylic acid esters;
fluorine-based resins such as polyvinylidene fluoride,
polytetrafluoroethylene and polyhexafluoropropylene; and
surfactants such as alkyl polyoxyethylene sulfates, alkyl benzene
sulfates, alkyl trimethyl ammonium salts, alkyl benzyldimethyl
ammonium salts, alkyl dimethylamine oxide, polyoxyethylene alkyl
ethers and fatty acid sorbitan esters. These additives are
decomposed and polymerized in the heat treating step performed
after the washing step, and thus they can be used to control the
surface of the lithium-containing composite oxide. Also, an acid or
alkali may be added to the water or organic solvent used for
washing. In this case, it is possible to obtain a more functional
material that contributes to control of processing conditions as
well as to reactions such as decomposition and polymerization of
the additive.
[0066] It is preferable to pulverize the baked composite oxide of
Li and the element group M prior to washing.
[0067] Next, the washed composite oxide of Li and the element group
M is subjected to a heat treatment. The heat treatment causes the
transition metals within the composite oxide to be reoriented and
allows the diffusion of Li within the composite oxide to proceed,
thereby stabilizing the valences of the transition metals present
in the whole composite oxide particles and on the surface
thereof.
[0068] In order to facilitate the diffusion of Li, the heat
treatment temperature is preferably 600.degree. C. or more at which
the Li-containing compound (for example, lithium carbonate) melts.
Also, in order to prevent the decomposition reaction of the
composite oxide, the heat treatment temperature is preferably
1000.degree. C. or less. The heat treatment time is preferably 1 to
24 hours. The heat treatment atmosphere is preferably an atmosphere
with an oxygen concentration of 18 vol % or more, and the heat
treatment may be performed in an atmosphere with an oxygen
concentration of 100 vol %.
[0069] The above-described production method of the present
invention enables stable production of lithium-containing composite
oxide particles that have a capacity of 150 mAh/g or more (relative
to Li metal, in the case of the driving voltage being 2.5 to 4.3 V)
and that can constitute a battery having excellent charge/discharge
cycle characteristics and storage characteristics.
[0070] The electrode for a non-aqueous secondary battery of the
present invention has an electrode material mixture layer using the
electrode active material (lithium-containing composite oxide
particles) of the present invention as an active material, and is
used as a positive electrode of a non-aqueous secondary
battery.
[0071] The electrode material mixture layer included in the
electrode of the present invention may contain an active material
other than the electrode active material of the present invention.
Examples of the active material other than the electrode active
material of the present invention include lithium cobalt oxides
such as LiCoO.sub.2; lithium manganese oxides such as LiMnO.sub.2
and Li.sub.2MnO.sub.3; lithium nickel oxides such as LiNiO.sub.2;
layer-structured lithium-containing composite oxides such as
LiCo.sub.1-xNiO.sub.2; spinel-structured lithium-containing
composite oxides such as LiMn.sub.2O.sub.4 and
Li.sub.4/3Ti.sub.5/3O.sub.4; olivine-structured lithium-containing
composite oxides such as LiFePO.sub.4; and the above-listed oxides
partially substituted with various elements. In the case of using
another active material, in order to clarify the effects of the
present invention, the ratio of the other active material is
desirably 30 mass % or less of the entire active material.
[0072] As the lithium cobalt oxide used as another active material,
it is preferable to use, in addition to LiCoO.sub.2 mentioned
above, oxides obtained by substituting a part of Co of LiCoO.sub.2
with at least one element selected from the group consisting of Ti,
Cr, Fe, Ni, Mn, Cu, Zn, Al, Ge, Sn, Mg and Zr (excluding the
lithium-containing composite oxide constituting the electrode
active material of the present invention). The reason for this is
that these lithium cobalt oxides have a high conductivity of
1.0.times.10.sup.-3 Scm.sup.-1 or more and can further increase the
load characteristics of the electrode.
[0073] As the spinel-structured lithium-containing composite oxide
used as another active material, in addition to LiMn.sub.2O.sub.4
and L.sub.4/3Ti.sub.5/3O.sub.4 mentioned above, it is preferable to
use oxides obtained by substituting a part of Mn of
LiMn.sub.2O.sub.4 with at least one element selected from the group
consisting of Ti, Cr, Fe, Ni, Co, Cu, Zn, Al, Ge, Sn, Mg and Zr
(excluding the lithium-containing composite oxide constituting the
electrode active material of the present invention). The reason for
this is that these spinel-structured lithium-containing composite
oxides are excellent in terms of safety during overcharge and the
like, further increasing the battery safety, because the amount of
lithium that can be extracted is 1/2 that of lithium-containing
oxides such as lithium cobalt oxide and lithium nickel oxide.
[0074] In the case where the electrode active material of the
present invention is used together with another active material,
they may be simply mixed, but it is more preferable to use the
active materials as composite particles by integrating the
particles of the active materials through granulation or the like.
In this case, the packing density of the active materials in the
electrode material mixture layer is improved, and the contact
between active material particles can be further ensured.
Accordingly, the capacity and the load characteristics of the
non-aqueous secondary battery using the electrode can be further
increased.
[0075] In the case of using the lithium-containing composite oxide
contained in the electrode active material of the present invention
that necessarily includes Mn as composite particles, the
lithium-containing cobalt oxide is present on the surface of the
lithium-containing composite oxide, and thus Mn and Co leached from
the composite particles rapidly deposit on the surface of the
composite particles, forming a coating film, and chemically
stabilizing the composite particles. This suppresses decomposition
of the non-aqueous electrolyte in the non-aqueous secondary battery
due to the composite particles, as well as further leaching of Mn,
and it is therefore possible to obtain a battery having excellent
charge/discharge cycle characteristics and storage
characteristics.
[0076] When the composite particles are used, it is preferable that
the number average particle size of either one of the electrode
active material of the present invention or another active material
is 1/2 or less the number average particle size of the other. In
the case of forming the composite particles by combining particles
having a large number average particle size (hereinafter referred
to as "large particles") and particles having a small number
average particle size (hereinafter referred to as "small
particles") as described above, the small particles are easily
dispersed and fixed around the large particles, and thus composite
particles having a more uniform mixing ratio can be formed.
Accordingly, non-uniform reactions in the electrode can be
suppressed, further increasing the charge/discharge cycle
characteristics and the safety of the battery.
[0077] When forming the composite particles using large particles
and small particles, the large particles preferably have a number
average particle size of 10 to 30 .mu.m, and the small particles
preferably have a number average particle size of 1 to 15
.mu.m.
[0078] The composite particles of the electrode active material of
the present invention and another active material can be obtained
by, for example, mixing the particles of the electrode active
material of the present invention and the particles of the other
active material with a commonly-used kneader such as a uniaxial
kneader or a biaxial kneader to rub the particles together, and
applying a shear force to composite the particles. Kneading is
preferably performed by a continuous kneading method that
continuously supplies raw material, in consideration of the
productivity of the composite particles.
[0079] It is preferable to add a binder to these active material
particles when kneading. It is thereby possible to well keep the
shape of the formed composite particles. It is more preferable to
add a conductive aid material when kneading. It is thereby possible
to further increase the conductivity between active material
particles.
[0080] As the binder that is added when the composite particles are
produced, any of thermoplastic resins and thermosetting resins can
be used as long as it is chemically stable within the non-aqueous
secondary battery. Examples include polyethylene, polypropylene,
polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),
polyhexafluoropropylene (PHFP), styrene butadiene rubber,
tetrafluoroethylene-hexafluoroethylene copolymers,
tetrafluoroethylene-hexafluoropropylene copolymers (FEP),
tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA),
vinylidene fluoride-hexafluoropropylene copolymers, vinylidene
fluoride-chlorotrifluoroethylene copolymers,
ethylene-tetrafluoroethylene copolymers (ETFE resin),
polychlorotrifluoroethylene (PCTFE), vinylidene
fluoride-pentafluoropropylene copolymers,
propylene-tetrafluoroethylene copolymers,
ethylene-chlorotrifluoroethylene copolymers (ECTFE), vinylidene
fluoride-hexafluoropropylene-tetrafluoroethylene copolymers,
vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene
copolymers or ethylene-acrylic acid copolymers,
ethylene-methacrylic acid copolymers, ethylene-methyl acrylate
copolymers, ethylene-methyl methacrylate copolymers, and Na ion
crosslinked structures of these copolymers. These may be used alone
or in a combination of two or more. Among them, it is preferable to
use PVDF, PTFE and PHFP in consideration of the stability in the
non-aqueous secondary battery and the characteristics of the
non-aqueous secondary battery. These may be used in combination, or
copolymers formed by these monomers may be used.
[0081] The amount of the binder added when forming the composite
particles is preferably as small as possible as long as it is
possible to stabilize the composite particles, and for example, the
amount of the binder is preferably 0.03 to 2 parts by mass based on
100 parts by mass of the total active materials.
[0082] As the conductive aid material added when the composite
particles are produced, any material can be used as long as it is
chemically stable within the non-aqueous secondary battery.
Examples include: graphites such as natural graphite and artificial
graphite; carbon blacks such as acetylene black, Ketjen Black
(trade name), channel black, furnace black, lamp black and thermal
black; conductive fibers such as carbon fiber and metal fiber;
metal powders such as aluminum powder; fluorinated carbon; zinc
oxide; conductive whisker made of potassium titanate or the like;
conductive metal oxides such as titanium oxide; and organic
conductive materials such as polyphenylene derivatives. These may
be used alone or m a combination two or more. Among them, it is
preferable to use graphites, which have a high conductivity or
carbon blacks, which have excellent liquid absorbing capabilities.
The form of the conductive aid material is not limited to primary
particles, and it is also possible to use secondary aggregates or
clusters such as chain structures. Such clusters are easy to
handle, and thus good productivity is obtained.
[0083] The amount of the conductive aid material added when forming
the composite particles can be any amount as long as good
conductivity and liquid absorbing capabilities can be ensured, and
for example, the amount of the conductive aid material is
preferably 0.1 to 2 parts by mass based on 100 parts by mass of the
total active materials.
[0084] The composite particles preferably have a porosity of 5 to
15%. The composite particles having such a porosity can be brought
into optimal contact with the non-aqueous electrolyte (non-aqueous
electrolytic solution), and the non-aqueous electrolyte can
optimally permeate into the composite particles.
[0085] Furthermore, the composite particles preferably have a
spherical shape or a substantially spherical shape as in the case
of the lithium-containing composite oxide particles of the
electrode active material of the present invention. It is thereby
possible to further increase the density of the electrode material
mixture layer.
[0086] The electrode of the present invention can be produced by,
for example, forming an electrode material mixture layer containing
the electrode active material or the composite particles of the
present invention as an active material on one or both sides of a
current collector.
[0087] The electrode material. mixture layer can be formed by, for
example, preparing an electrode material mixture-containing
composition in the form of a paste or a slurry by adding the
electrode active material or the composite particles of the present
invention, a binder and a conductive aid material to a solvent, and
applying the electrode material mixture-containing composition onto
the surface of a current collector by any application method,
drying and pressing the current collector to adjust the thickness
and the density of the electrode material mixture layer.
[0088] The application method used to apply the electrode material
mixture-containing composition onto the surface of a current
collector can be, for example, a substrate withdrawing method using
a doctor blade, a coater method using a die coater, a comma coater,
a knife coater or the like, a printing method such as screen
printing or relief printing.
[0089] As the binder and the conductive aid material that can be
used to prepare the electrode material mixture-containing
composition, any of various binders and various conductive aid
materials listed above used to form the composite particles can be
used.
[0090] The electrode material mixture layer preferably contains 80
to 99 mass % of active materials including the electrode active
material of the present invention, (15 to 10 mass % of a binder
(including the binder contained in the composite particles), and
0.5 to 10 mass % of a conductive aid material (including the
conductive aid material contained in the composite particles).
[0091] It is preferable that the electrode material mixture layer
formed on one side of a current collector has a thickness after
pressing of 15 to 200 .mu.m. Furthermore, the electrode material
mixture layer preferably has a density after pressing of 3.2
g/cm.sup.3 or more, and more preferably 3.5 g/cm.sup.3 or more.
With an electrode including such an electrode material mixture
layer having a high density, a high capacity can be achieved.
However, if the density of the electrode material mixture layer is
too high, the porosity will be low, and the permeability of the
non-aqueous electrolyte may decrease. Accordingly, the electrode
material mixture layer preferably has a density after pressing of
3.8 g/cm.sup.3 or less. Pressing can be performed by, for example,
roll pressing at a line pressure of approximately 1 to 100 kN/cm.
Through this process, an electrode material mixture layer having
the above-described density can be obtained.
[0092] The density of the electrode material mixture layer as used
herein refers to a value measured by the following method. Firstly,
the electrode is cut into a piece having a certain area, the mass
of the piece is measured using an electrobalance with a minimum
scale value of 0.1 mg, and the mass of the electrode material
mixture layer is calculated by subtracting the mass of the current
collector from the mass of the electrode piece. Meanwhile, the
total thickness of the electrode is measured at ten points using a
micrometer with a minimum scale value of 1 .mu.m, and the volume of
the electrode material mixture layer is calculated from the area
and the average of values obtained by subtracting the current
collector thickness from these measured values. Then, the density
of the electrode material mixture layer is calculated by dividing
the mass of the electrode material mixture layer by the volume.
[0093] There is no particular limitation on the material of the
current collector used in the electrode as long as an electronic
conductor that is chemically stable in the formed non-aqueous
secondary battery is used. Examples include aluminum, an aluminum
alloy, stainless steel, nickel, titanium, carbon, and a conductive
resin. It is also possible to use a composite material in which a
carbon layer or a titanium layer is formed on the surface of
aluminum, an aluminum alloy or stainless steel. Among them, it is
particularly preferable to use aluminum or an aluminum alloy
because these materials are lightweight and have high electron
conductivity. As the electrode current collector, for example, a
foil, a film, a sheet, a net, a punched sheet, a lath, a porous
sheet, a foam, and a molded article formed of fiber bundle that are
made of any of the above-listed materials can be used. It is also
possible to roughen the current collector surface by surface
treatment. There is no particular limitation on the thickness of
the current collector, but the thickness is usually 1 to 500
.mu.m.
[0094] The electrode of the present invention is not limited to the
electrode produced by the above production method, and may be an
electrode produced by other methods. The electrode of the present
invention can be, for example, in the case of using the composite
particles as an active material, an electrode obtained by a method
in which the composite particles are directly fixed to the current
collector surface to form an electrode material mixture layer,
without using the electrode material mixture-containing
composition.
[0095] In the electrode of the present invention, a lead connector
for electrically connecting to other members within the non-aqueous
secondary battery may be formed by a conventional method as
needed.
[0096] The non-aqueous secondary battery of the present invention
includes the electrode for a non-aqueous secondary battery of the
present invention as a positive electrode. There is no particular
limitation on the configuration and the structure of other
elements, and conventionally known configuration and structure
employed in non-aqueous secondary batteries can be used.
[0097] As the negative electrode, a negative electrode having, for
example, a negative electrode material mixture layer made of a
negative electrode material mixture containing a negative electrode
active material, a binder and optionally a conductive aid material
on one or both sides of a current collector can be used.
[0098] Examples of the negative electrode active material include
graphite, pyrolytic carbon, coke, glassy carbon, baked products of
organic polymer compounds, mesocarbon microbeads, carbon fiber,
activated carbon, metals capable of being alloyed with lithium (Si,
Sn and the like), and alloys thereof. As the binder and the
conductive aid material, any of the binders and conductive aid
materials listed above for use in the electrode of the present
invention can be used.
[0099] There is no particular limitation on the material of the
negative electrode current collector as long as an electronic
conductor that is chemically stable in the formed battery is used.
Examples include copper, a copper alloy, stainless steel, nickel,
titanium, carbon, and a conductive resin. It is also possible to
use a composite material in which a carbon layer or a titanium
layer is formed on the surface of copper, a copper alloy or
stainless steel. Among them, it is particularly preferable to use
copper or a copper alloy because these materials are not alloyed
with lithium and have high electron conductivity. As the negative
electrode current collector, for example, a foil, a film, a sheet,
a net, a punched sheet, a lath, a porous sheet, a foam, and a
molded article formed of fiber bundle that are made of any of the
above-listed materials can be used. It is also possible to roughen
the current collector surface by surface treatment. There is no
particular limitation on the thickness of the current collector,
but the thickness is usually 1 to 500 .mu.m.
[0100] The negative electrode can be obtained by, for example,
applying a negative electrode material mixture-containing
composition in the form of a paste or a slurry obtained by
dispersing a negative electrode material mixture containing a
negative electrode active material, a binder and optionally a
conductive aid material in a solvent (the binder may be dissolved
in the solvent) on one or both sides of a current collector, and
drying the current collector so as to form a negative electrode
material mixture layer. The negative electrode is not limited to
the negative electrode obtained by the above-described production
method, and may be a negative electrode produced by other methods.
The negative electrode material mixture layer formed on one side of
the current collector is preferably 10 to 300 .mu.m.
[0101] The separator is preferably a porous film formed of a
polyolefin such as polyethylene, polypropylene or
ethylene-propylene copolymer, a polyester such as polyethylene
terephthalate or copolymerized polyester, or the like. The
separator preferably has a property that closes the pores at 100 to
140.degree. C. (or in other words, a shutdown function).
Accordingly, it is more preferable that the separator contains, as
a component, a thermoplastic resin having a melting point of 100 to
140.degree. C., measured using a differential scanning calorimeter
(DSC) in accordance with Japanese Industrial Standard (JIS) K 7121,
and the separator is preferably a monolayer porous film containing
polyethylene as a main component, or a laminated porous film
constituted of porous films such as a laminated porous film in
which two to five layers made of polyethylene and polypropylene are
laminated. In the case of mixing polyethylene with a resin having a
melting point higher than that of a polyethylene such as
polypropylene, or laminating these, it is desirable to use 30 mass
% or more of polyethylene, and more desirably 50 mass % or more as
the resin that constitutes the porous film.
[0102] As the resin porous film, for example, it is possible to use
a porous film made of any of the above-listed thermoplastic resins
used in conventionally known non-aqueous secondary batteries and
the like, or in other words, an ion permeable porous film produced
by a solvent extraction method, a dry or wet drawing method, or the
like.
[0103] The separator preferably has an average pore size of 0.01
.mu.m or more, and more preferably 0.05 .mu.m or more, and
preferably 1 .mu.m or less, and more preferably 0.5 .mu.m or
less.
[0104] As the characteristics of the separator, it is desirable
that the separator has a Gurley value of 10 to 500 sec, measured by
the method in accordance with JIS P 8117, the Gurley value
indicating the time, expressed in seconds, required for 100 mL of
air to pass through a film under pressure of 0.879 g/mm.sup.2. If
the air permeability is too high, the ion permeability will be
reduced. If, on the other hand, the permeability is too low, the
strength of the separator may be reduced. Furthermore, as the
strength of the separator, it is desirable that the separator has a
piercing strength of 50 g or more, measured using a needle with a
diameter of 1 mm. If the piercing strength is too small,
short-circuiting may occur due to the separator being penetrated
and broken by formation of lithium dendrite crystals.
[0105] Even if the internal temperature of the non-aqueous
secondary battery reaches 150.degree. C. or more, the
lithium-containing composite oxide particles included in the
electrode active material of the present invention have excellent
thermal stability, and thus safety can be maintained.
[0106] As the non-aqueous electrolyte, a solution (non-aqueous
electrolytic solution) in which an electrolyte salt is dissolved in
an organic solvent can be used. Examples of the solvent include EC,
PC, BC, DMC, DEC, MEC, .gamma.-butyrolactone, 1,2-dimethoxyethane,
tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide,
1,3-dioxolane, formamide, dimethylformamide, dioxolane,
acetonitrile, nitromethane, methyl formate, methyl acetate,
phosphoric triester, trimethoxymethane, a dioxolane derivative,
sulfolane, 3-methyl-2-oxazolidinone, a propylene carbonate
derivative, a tetrahydrofuran derivative, diethyl ether, and an
aprotic organic solvent such as 1,3-propane sultone. These may be
used alone or in a combination of two or more. It is also possible
to use an aminimide-based organic solvent, a sulfur-containing
organic solvent, a fluorine-containing organic solvent, or the
like. Among them, it is preferable to use a solvent mixture of EC,
MEC and DEC. In this case, it is more preferable that DEC is
contained in an amount of 15 vol % or more and 80 vol % or less
based on the total volume of the solvent mixture. This is because
with such a solvent mixture, it is possible to maintain the
low-temperature characteristics and the charge/discharge cycle
characteristics of the battery at high levels, and enhance the
stability of the solvent during high-voltage charging.
[0107] As the electrolyte salt used in the non-aqueous electrolyte
described above, a lithium perchlorate, an organic boron lithium
salt, a salt of a fluorine-containing compound such as
trifluoromethane sulfonate, an imide salt, or the like is suitably
used. Specific examples of the electrolyte salt include
LiClO.sub.4, LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6, LiSbF.sub.6,
LiCF.sub.3SO.sub.3, LiC.sub.4F.sub.9SO.sub.3, LiCF.sub.3CO.sub.2,
Li.sub.2C.sub.2F.sub.4(SO.sub.3).sub.2,
LiN(CF.sub.3SO.sub.2).sub.2, LiC(CF.sub.3SO.sub.2).sub.3,
LiC.sub.nF.sub.2n+1SO.sub.3 (2.ltoreq.n.ltoreq.7), and
LiN(Rf.sub.3OSO.sub.2).sub.2, where Rf represents a fluoroalkyl
group. These may be used alone or in a combination of two or more.
Among them, it is more preferable to use LiPF.sub.6, LiBF.sub.4, or
the like because they provide good charge/discharge
characteristics. This is because these fluorine-containing organic
lithium salts are easily soluble in the above-listed solvents as
they have a high anionic character and easily undergo ion
separation. There is no particular limitation on the concentration
of the electrolyte salt in the solvent, and the concentration is
0.5 to 1.7 mol/L.
[0108] It is also possible to add an additive to the non-aqueous
electrolyte as appropriate such as vinylene carbonate, 1,3-propane
sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl,
fluorobenzene, or t-butyl benzene, for the purpose of improving the
characteristics such as safety, charge/discharge cycle
characteristics, and high temperature storage characteristics. It
is particularly preferable to add an additive containing the
element sulfur because the surface activity of the active material
containing Mn can be stabilized.
[0109] The non-aqueous secondary battery of the present invention
is formed by, for example, producing a laminate electrode assembly
in which the electrode of the present invention and a negative
electrode as described above are laminated with a separator as
described above interposed therebetween or a wound electrode
assembly obtained by spirally winding the laminate electrode
assembly, and enclosing the electrode assembly and a non-aqueous
electrolyte as described above in an outer case by a conventional
method. As the form of the battery, as in the case of
conventionally known non-aqueous secondary batteries, the battery
can be a cylindrical battery using a cylindrical (circular cylinder
or rectangular cylinder) outer case can, a flat battery using a
flat (flat circle or flat rectangular as viewed from above) outer
case can, a soft package battery using a laminated film having a
metal deposited thereon as an outer case. As the outer case can, a
steel or aluminum may be used.
EXAMPLES
[0110] Hereinafter, the present invention will be described in
detail by way of examples. It should be noted, however, that the
examples given below are not intended to limit the present
invention.
Example 1
Production of Electrode Active Material
[0111] A coprecipitated compound (spherical coprecipitated
compound) containing Ni, Co and Mn was synthesized by placing, in a
reaction vessel, ammonia water having a pH adjusted to
approximately 12 by addition of sodium hydroxide, and then, while
strongly stirring, adding dropwise a mixed aqueous solution
containing nickel sulfate, cobalt sulfate and manganese sulfate at
concentrations of 2.4 mol/dm.sup.3, 0.8 mol/dm.sup.3 and 0.8
mol/dm.sup.3, and 25 mass % of ammonia water at rates of 23
cm.sup.3/min and 6.6 cm.sup.3/min, respectively, using a metering
pump. At this time, the temperature of the reactant solution was
held at 50.degree. C., an aqueous solution of sodium hydroxide
having a concentration of 6.4 mol/dm.sup.3 was also added dropwise
such that the pH of the reactant solution was maintained at around
12, and a nitrogen gas was bubbled at a flow rate of 1 dm.sup.3/min
in order to carry out the reaction in an inert atmosphere.
[0112] The synthesized coprecipitated compound was washed with
water, filtrated and dried to obtain a hydroxide containing Ni, Co
and Mn at a molar ratio of 6:2:2. The obtained hydroxide in an
amount of 0.196 mol and 0.204 mol of LiOH.H.sub.2O were dispersed
in ethanol to form a slurry, and the slurry was mixed for 40
minutes using a planetary ball mill and dried at room temperature
to obtain a mixture. Subsequently, the mixture was placed in an
alumina crucible, heated to 600.degree. C. in a dry air flow of 2
dm.sup.3/min, held at that temperature for two hours for
preheating, and baked for 12 hours by increasing the temperature to
900.degree. C. A lithium-containing composite oxide was thereby
synthesized.
[0113] The obtained lithium-containing composite oxide was washed
with water, heat treated in the atmospheric air (with an oxygen
concentration of approximately 20 vol %) at 850.degree. C. for 12
hours, and then pulverized into powder using a mortar, thereby
obtaining an electrode active material. The obtained electrode
active material was stored in a desiccator.
[0114] The electrode active material (lithium-containing composite
oxide powder) was analyzed for its composition by an atomic
absorption spectrometer, and was found to have a composition
represented by Li.sub.1.02Ni.sub.0.60Co.sub.0.20Mn.sub.0.20O.sub.2,
(x=0.02, d=0.2, e=0.2 in the general compositional formula
(2)).
[0115] In order to perform state analysis of the lithium-containing
composite oxide, X-ray absorption spectroscopy (XAS) was performed
using BL4 beam port of compact superconducting radiation source
Aurora available from Sumitomo Electric Industries, Ltd. installed
at the SR Center of Ritsumeikan University. The average valence of
each of the elements included in the whole particles was measured
by XAS using a transmission method, and the valence of each element
on the particle surface was measured by an electron yield method.
The obtained data was analyzed by using analysis software REX
available from Rigaku Corporation based on Journal of the
Electrochemical. Society 146, p 2799-2809 (1999).
[0116] Firstly, in order to determine the average valence of Ni in
the whole lithium-containing composite oxide powder, state analysis
similar to that performed on the lithium-containing composite oxide
powder was performed using NiO and LiNi.sub.0.5Mn.sub.1.5O.sub.4
(standard samples for compounds containing Ni having an average
valence of 2) and LiNi.sub.0.82Co.sub.0.15Al.sub.0.03O.sub.2 (a
standard sample for a compound containing Ni having an average
valence of 3), and a regression line representing the relationship
between the position of the K absorption edge of Ni and the valence
of Ni was created for each standard sample.
[0117] The state analysis of the lithium-containing composite oxide
powder found, from the position of the K absorption edge of Ni,
that the average valence of Ni in the lithium-containing composite
oxide was 2.72. Also, the measurement using an electron yield
method found, from the position of the K absorption edge of Ni,
that the valence of Ni on the powder surface of the
lithium-containing composite oxide was 2.57.
[0118] The average valence of Co in the whole powder and the
valence of Co on the powder surface were determined in the same
manner as the average valence of Ni in the whole powder and the
valence of Ni on the powder surface after creating a regression
line similar to that created for Ni, using CoO (a standard sample
for a compound containing Co having an average valence of 2) and
LiCoO.sub.2 (a standard sample for a compound containing Co having
an average valence of 3).
[0119] The average valence of Mn in the whole powder and the
valence of Mn on the powder surface were determined in the same
manner as the average valence of Ni in the whole powder and the
valence of Ni on the powder surface after creating a regression
line similar to that created for Ni, using MnO.sub.2 and
LiNi.sub.0.5Mn.sub.1.5O.sub.4 (standard samples for compounds
containing Mn having an average valence of 4), LiMn.sub.2O.sub.4 (a
standard sample for a compound containing Mn having an average
valence of 3.5), LiMnO.sub.2 and Mn.sub.2O.sub.3 (standard samples
for compounds containing Mn having an average valence of 3) and MnO
(a standard sample for a compound containing Mn having an average
valence of 2.
Production of Positive Electrode
[0120] A positive electrode material mixture-containing paste was
prepared by kneading 100 parts by mass of the above electrode
active material, 20 parts by mass of an N-methyl-2-pyrrolidone
(NMP) solution containing PVDF as a binder at a concentration of 10
mass %, 1 part by mass of artificial graphite as a conductive aid
material and 1 part by mass of ketjen black with the use of a
biaxial kneader and then adding NMP for viscosity adjustment.
[0121] The prepared positive electrode material mixture-containing
paste was applied to both sides of a 15 .mu.m thick aluminum foil
(positive electrode current collector), and then vacuum-dried at
120.degree. C. for 12 hours to form positive electrode material
mixture layers on both sides of the aluminum foil. After that,
pressing was performed to adjust the thickness and density of the
positive electrode material mixture layers, a lead connector made
of nickel was welded to an exposed portion of the aluminum foil,
and a strip-shaped positive electrode having a length of 375 mm and
a width of 43 mm was produced. In the obtained positive electrode,
each positive electrode material mixture layer had a thickness of
55 .mu.m.
Production of Negative Electrode
[0122] A negative electrode material mixture-containing paste was
prepared by adding water to 97.5 parts by mass of natural graphite
having a number average particle size of 10 .mu.m as a negative
electrode active material, 1.5 parts by mass of styrene butadiene
rubber as a binder and 1 part by mass of carboxymethyl cellulose as
a thickener and mixing them. The prepared negative electrode
material mixture-containing paste was applied to both sides of a 8
.mu.m thick copper foil, and then vacuum-dried at 120.degree. C.
for 12 hours to form negative electrode material mixture layers on
both sides of the copper foil. After that, pressing was performed
to adjust the thickness and density of the negative electrode
material mixture layers, a lead connector made of nickel was welded
to an exposed portion of the copper foil, and a strip-shaped
negative electrode having a length of 380 mm and a width of 44 mm
was produced. In the obtained negative electrode, each negative
electrode material mixture layer had a thickness of 65 .mu.m.
[0123] Preparation of Non-Aqueous Electrolyte
[0124] A non-aqueous electrolyte was prepared by dissolving
LiPF.sub.6 at a concentration of 1 mol/L in a solvent mixture of
EC, MEC and DEC at a volume ratio of 2:3:1.
[0125] Assembly of Battery
[0126] The strip-shaped positive electrode was laminated on the
strip-shaped negative electrode with a 16 .mu.m thick microporous
polyethylene separator (porosity: 41%) interposed therebetween,
these were spirally wound and pressed into a flat shape to obtain a
flat wound electrode assembly, and the obtained wound electrode
assembly was fixed with polypropylene insulation tape. Next, the
wound electrode assembly was inserted in a prismatic battery case
made of an aluminum alloy having a thickness of 4.0 mm, a width of
34 mm and a height of 50 mm, lead connectors were welded, and a lid
plate made of an aluminum alloy was welded to the opening edge of
the battery case. After that, the non-aqueous electrolyte was
injected from an inlet provided in the lid plate, and after
standing one hour, the inlet was sealed to obtain a non-aqueous
secondary battery having the structure shown in FIGS. 1A and 1B and
the outer appearance shown in FIG. 2. The designed electrical
capacity of the non-aqueous secondary battery was 1000 mAh.
[0127] The battery shown in FIGS. 1A, 1B and 2 will be described
here. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view
of FIG. 1A. As shown in FIG. 1B, a positive electrode 1 and a
negative electrode 2 are spirally wound with a separator 3
interposed therebetween, and then pressed into a flat shape to form
a flat wound electrode assembly 6, and the electrode assembly 6 is
housed in a rectangular cylindrical battery case 4 together with a
non-aqueous electrolyte. In order to simplify the illustration of
FIG. 1B, metal foils serving as current collectors used to produce
the positive electrode 1 and the negative electrode 2 and the
non-aqueous electrolyte are not illustrated.
[0128] The battery case 4 is a battery outer case made of an
aluminum alloy, and the battery case 4 also serves as a positive
electrode terminal. An insulator 5 made of a polyethylene sheet is
placed on the bottom of the battery case 4, and a positive
electrode lead connector 7 and a negative electrode lead connector
8 connected to the ends of the positive electrode 1 and the
negative electrode 2, respectively, are drawn from the flat wound
electrode assembly 6 including the positive electrode 1, the
negative electrode 2 and the separator 3. A stainless steel
terminal 11 is attached to a sealing lid plate 9 made of an
aluminum alloy for sealing the opening of the battery case 4 with a
polypropylene insulation packing 10 interposed therebetween, and a
stainless steel lead plate 13 is attached to the terminal 11 with
an insulator 12 interposed therebetween.
[0129] Then, the lid plate 9 is inserted into the opening of the
battery case 4, the joint ortions of the lid plate 9 and the
battery case 4 are welded to seal the opening the battery case 4,
and thereby the interior of the battery is sealed. In the battery
shown in FIGS. 1A and 1B, the lid plate 9 is provided with a
non-aqueous electrolyte inlet 14, and the non-aqueous electrolyte
inlet 14 is sealed by welding such as, for example, laser welding,
with a sealing member inserted into the non-aqueous electrolyte
inlet 14, and thereby the seal of the battery is ensured.
Accordingly, in the battery shown in FIGS. 1A, 1B and 2, the
non-aqueous electrolyte inlet 14 actually includes the non-aqueous
electrolyte inlet and the sealing member, but in order to simplify
the illustration, they are indicated as the non-aqueous electrolyte
inlet 14. The lid plate 9 is also provided with a rupture vent 15
serving as a mechanism that discharges internal gas to the outside
in the event of overheating of the battery
[0130] In the battery of Example 1, the positive electrode lead
connector 7 is welded directly to the lid plate 9, whereby the
battery case 4 and the lid plate 9 function as a positive electrode
terminal. Likewise, the negative electrode lead connector 8 is
welded to the lead plate 13, and the negative electrode lead
connector 8 and the terminal 11 are electrically connected via the
lead plate 13, whereby the terminal 11 functions as a negative
electrode terminal.
[0131] FIG. 2 is a perspective view schematically showing the outer
appearance of the battery shown in FIG. 1A, and FIG. 2 is
illustrated to indicate that the battery is a prismatic battery.
FIG. 2 schematically shows the battery, and thus only specific
constituent elements of the battery are shown. Similarly, in FIG.
1B, the innermost portion of the electrode assembly is not shown in
cross section.
Example 2
[0132] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
a hydroxide containing Ni, Co and Mn at a molar ratio of 6:3:1 was
synthesized by adjusting the concentrations of the raw material
compounds of the mixed aqueous solution used to synthesize the
coprecipitated compound, and the synthesized hydroxide was used.
Furthermore, a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Example 3
[0133] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
a hydroxide containing Ni, Co and Mn at a molar ratio of 6:1:3 was
synthesized by adjusting the concentrations of the raw material
compounds of the mixed aqueous solution used to synthesize the
coprecipitated compound, and the synthesized hydroxide was used.
Furthermore, a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Example 4
[0134] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
a hydroxide containing Ni, Co and Mn at a molar ratio of 5.5:1.5:3
was synthesized by adjusting the concentrations of the raw material
compounds of the mixed aqueous solution used to synthesize the
coprecipitated compound, and the synthesized hydroxide was used.
Furthermore, a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Example 5
[0135] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
a hydroxide containing Ni, Co and Mn at a molar ratio of 5.5:2:2.5
was synthesized by adjusting the concentrations of the raw material
compounds of the mixed aqueous solution used to synthesize the
coprecipitated compound, and the synthesized hydroxide was used.
Furthermore, a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Example 6
[0136] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
a hydroxide containing Ni, Co and Mn at a molar ratio of 5:2:3 was
synthesized by adjusting the concentrations of the raw material
compounds of the mixed aqueous solution used to synthesize the
coprecipitated compound, and the synthesized hydroxide was used.
Furthermore, a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Example 7
[0137] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
a hydroxide containing Ni, Co and Mn at a molar ratio of 5:3:2 was
synthesized by adjusting the concentrations of the raw material
compounds of the mixed aqueous solution used to synthesize the
coprecipitated compound, and the synthesized hydroxide was used.
Furthermore, a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Comparative Example 1
[0138] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
the water washing after baking and the heat treatment were not
performed, and a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 1, except
that the produced electrode active material was used.
Comparative Example 2
[0139] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 2, except that
the water washing after baking and the heat treatment were not
performed, and a positive electrode and a non-aqueous secondary
battery were produced in the same manner as in Example 2, except
that the produced electrode active material was used.
Comparative Example 3
[0140] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
the heat treatment after water washing was performed in a nitrogen
atmosphere, or in other words, in an oxygen-free atmosphere, and a
positive electrode and a non-aqueous secondary battery were
produced in the same manner as in Example 1, except that the
produced electrode active material was used.
Comparative Example 4
[0141] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 2, except that
the temperature of the heat treatment after water washing was set
to 500.degree. C., and a positive electrode and a non-aqueous
secondary battery were produced in the same manner as in Example 1,
except that the produced electrode active material was used.
Comparative Example 5
[0142] An electrode active material (lithium-containing composite
oxide) was produced in the same manner as in Example 1, except that
the temperature of the heat treatment after water washing was set
to 1100.degree. C., and a positive electrode and a non-aqueous
secondary battery were produced in the same manner as in Example 1,
except that the produced electrode active material was used.
Comparative Example 6
[0143] A positive electrode and a non-aqueous secondary battery
were produced in the same manner as in Example 1, except that
commercially available
Li.sub.1.02Ni.sub.0.80Co.sub.0.15Al.sub.0.05O.sub.2 was used as an
active material.
[0144] Composition, average valence of each of Ni, Co and Mn in the
whole powder and valence of each of Ni, Co and Mn on the powder
surface were determined for the electrode active materials of
Examples 2 to 7 and Comparative Examples 1 to 6 in the same manner
as in Example 1. Table 1 shows the compositions of the electrode
active materials (lithium-containing composite oxides) produced in
Examples 1 to 7 and Comparative Examples 1 to 6. Table 2 shows the
average valence of each of Ni, Co and Mn in the whole powder and
the valence of each of Ni, Co and Mn on the powder surface for the
electrode active materials (lithium-containing composite oxides)
produced in Examples 1 to 7 and Comparative Examples 1 to 6.
TABLE-US-00001 TABLE 1 Composition of lithium-containing composite
oxide Compositional formula x a b c Ex. 1
Li.sub.1.02Ni.sub.0.60Co.sub.0.20Mn.sub.0.20O.sub.2 0.02 60 20 20
Ex. 2 Li.sub.1.02Ni.sub.0.60Co.sub.0.30Mn.sub.0.10O.sub.2 0.02 60
30 10 Ex. 3 Li.sub.1.02Ni.sub.0.60Co.sub.0.10Mn.sub.0.30O.sub.2
0.02 60 10 30 Ex. 4
Li.sub.1.02Ni.sub.0.55Co.sub.0.15Mn.sub.0.30O.sub.2 0.02 55 15 30
Ex. 5 Li.sub.1.02Ni.sub.0.55Co.sub.0.20Mn.sub.0.25O.sub.2 0.02 55
20 25 Ex. 6 Li.sub.1.02Ni.sub.0.50Co.sub.0.20Mn.sub.0.30O.sub.2
0.02 50 20 30 Ex. 7
Li.sub.1.02Ni.sub.0.50Co.sub.0.30Mn.sub.0.20O.sub.2 0.02 50 30 20
Comp. Ex. 1 Li.sub.1.02Ni.sub.0.60Co.sub.0.20Mn.sub.0.20O.sub.2
0.02 60 20 20 Comp. Ex. 2
Li.sub.1.02Ni.sub.0.60Co.sub.0.30Mn.sub.0.10O.sub.2 0.02 60 30 10
Comp. Ex. 3 Li.sub.0.92Ni.sub.0.60Co.sub.0.20Mn.sub.0.20O.sub.1.8
-0.08 60 20 20 Comp. Ex. 4
Li.sub.1.02Ni.sub.0.60Co.sub.0.30Mn.sub.0.10O.sub.2 0.02 60 30 10
Comp. Ex. 5 Li.sub.0.88Ni.sub.0.60Co.sub.0.20Mn.sub.0.20O.sub.2
-0.12 60 20 20 Comp. Ex. 6
Li.sub.1.02Ni.sub.0.80Co.sub.0.15Al.sub.0.05O.sub.2 0.02 80 15
--
[0145] In Table 1, x in the composition of lithium-containing
composite oxide represents x in the general compositional formulas
(1) and (2). Similarly, a, b and c respectively represent the
ratios (mol %) of Ni, Co and Mn based on the total amount of the
element group M taken as 100 mol %. The units are omitted in Table
1.
TABLE-US-00002 TABLE 2 Ni valence Co valence Mn valence Average
Valence on Average Valence on Average Valence on valence powder
surface valence powder surface valence powder surface Ex. 1 2.72
2.57 2.79 2.65 4.07 4.05 Ex. 2 2.73 2.59 2.74 2.60 4.07 4.05 Ex. 3
2.53 2.40 2.78 2.55 4.07 4.05 Ex. 4 2.48 2.38 2.78 2.55 4.07 4.05
Ex. 5 2.64 2.51 2.88 2.65 4.07 4.05 Ex. 6 2.40 2.16 2.76 2.55 4.07
4.05 Ex. 7 2.62 2.56 2.80 2.65 4.07 4.05 Comp. Ex. 1 2.72 2.59 2.79
3.12 4.07 4.05 Comp. Ex. 2 2.73 2.61 2.74 3.08 4.07 4.05 Comp. Ex.
3 2.52 2.55 2.61 2.64 3.72 3.74 Comp. Ex. 4 2.72 2.70 2.79 2.91
4.07 4.05 Comp. Ex. 5 2.61 2.60 2.70 2.72 4.07 4.05 Comp. Ex. 6
3.00 2.90 3.05 3.01 -- --
[0146] The non-aqueous secondary batteries of Examples 1 to 7 and
Comparative Examples 1 to 6 were subjected to the following
evaluations. The results are shown in Table 3.
[0147] Capacity Measurement
[0148] Each of the batteries of Examples 1 to 7 and Comparative
Examples 1 to 6 was stored at 60.degree. C. for 7 hours, and
thereafter a charge/discharge cycle in which the battery was
charged at a current value of 200 mA for 5 hours and discharged at
a current value of 200 mA to a battery voltage of 3 V was repeated
at 20.degree. C. until the discharge capacity became constant.
Subsequently, constant current-constant voltage charge (constant
current: 500 mA, constant voltage: 4.2 V, total charge time: 3
hours) was performed, after a rest period of one hour, the battery
was discharged at a current value of 200 mA to a battery voltage of
3 V, and standard capacity was determined. For each of the examples
and comparative examples, 100 batteries were measured and the
average value was taken as the standard capacity of the example or
comparative example.
[0149] Charge/Discharge Cycle Characteristics
[0150] Each of the batteries of Examples 1 to 7 and Comparative
Examples 1 to 6 was subjected to repeated charge/discharge cycles
in which constant current-constant voltage charge was performed
under the same conditions as those for the standard capacity
measurement, and after a rest period of one minute, discharge was
performed at a current value of 200 mA to a battery voltage of 3 V,
so as to obtain the number of cycles at which the discharge
capacity decreased to 70% of the initial discharge capacity, and
thereby the charge/discharge cycle characteristics of each battery
was evaluated. The number of cycles mentioned in the description of
charge/discharge cycle characteristics was measured for 10
batteries for each of the examples and comparative examples, and
the average value was taken as the number of cycles of the example
or comparative example.
[0151] Storage Characteristics
[0152] Each of the batteries of Examples 1 to 7 and Comparative
Examples 1 to 6 was subjected to constant current-constant voltage
charge (constant current: 400 mA, constant voltage: 4.25 V, total
charge time: 3 hours), and then was placed and allowed to sit in a
constant temperature chamber at 80.degree. C. for 5 days. Then, the
thickness of the battery was measured. Storage characteristics were
evaluated based on the battery bulge during storage determined by
the difference between the thickness after storage of each battery
obtained in the above-described manner and the thickness before
storage (4.0 mm).
[0153] Safety Evaluation
[0154] Each of the batteries of Examples 1 to 7 and Comparative
Examples 1 to 6 was subjected to constant current-constant voltage
charge (constant current: 1000 mA, constant voltage: 4.25 V, total
charge time: 3 hours), thereafter the battery was placed in a
constant temperature chamber, after a rest period of two hours, the
temperature was increased from 30.degree. C. to 170.degree. C. at a
rate of 5.degree. C. per minute, the battery was subsequently
allowed to sit at 170.degree. C. for 3 hours, and then the surface
temperature of the battery was measured. Batteries with a highest
battery surface temperature of 180.degree. C. or less were rated as
A, and batteries with a highest battery surface temperature
exceeding 180.degree. C. were rated as B.
TABLE-US-00003 TABLE 3 Standard Number of capacity cycles Battery
bulge (mAh) (times) during storage Safety Ex. 1 987 540 0.70 A Ex.
2 980 550 0.72 A Ex. 3 955 520 0.80 A Ex. 4 934 600 0.65 A Ex. 5
940 580 0.54 A Ex. 6 900 640 0.45 A Ex. 7 920 620 0.40 A Comp. Ex.
1 978 426 1.24 A Comp. Ex. 2 974 443 1.26 A Comp. Ex. 3 448 125
1.60 A Comp. Ex. 4 968 467 1.07 A Comp. Ex. 5 636 321 1.16 A Comp.
Ex. 6 971 473 1.12 B
[0155] The non-aqueous secondary batteries of Examples 1 to 7,
which had a positive electrode using, as an active material, a
lithium-containing composite oxide in which the average valences of
Ni, Co and Mn in the whole powder were optimal, and the valences of
Ni and Co on the powder surface were smaller than the average Ni
valence and the average Co valence, exhibited a large standard
capacity, excellent safety, good charge/discharge cycle
characteristics and storage characteristics.
[0156] In contrast, the non-aqueous secondary batteries of
Comparative Examples 1, 2, 4 and 5, which had a positive electrode
using, as an active material, a lithium-containing composite oxide
in which the valence of Co on the powder surface was higher than
the average valence of Co in the whole powder, exhibited poor
charge/discharge cycle characteristics and storage characteristics,
and the non-aqueous secondary battery of Comparative Example 5 also
exhibited a small standard capacity. The non-aqueous secondary
battery of Comparative Example 3, which had a positive electrode
using, as an active material, a lithium-containing composite oxide
in which the valences of Ni and Co on the powder surface were
higher than the average valence of Ni and the average valence of Co
in the whole powder, exhibited a small standard capacity, and poor
charge/discharge cycle characteristics and storage characteristics.
Furthermore, the non-aqueous secondary battery of Comparative
Example 6, which had a positive electrode using, as an active
material, commercially available
Li.sub.1.02Ni.sub.0.80Co.sub.0.15Al.sub.0.05O.sub.2 and containing
no Mn, exhibited poor charge/discharge cycle characteristics,
storage characteristics and safety.
[0157] The invention may be embodied in other forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not limiting. The scope of the
invention is indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are intended to be
embraced therein.
INDUSTRIAL APPLICABILITY
[0158] According to the present invention, it is possible to
provide a non-aqueous secondary battery that has a high capacity,
good safety even in high temperature environments, and excellent
charge/discharge cycle characteristics and storage characteristics.
The non-aqueous secondary battery of the present invention can be
used in applications such as power sources for various electronic
devices including portable electronic devices such as cell phones
and notebook personal computers, and can also be used in
applications that require safety such as electric tools,
automobiles, bicycles and power storages.
DESCRIPTION OF REFERENCE NUMERALS
[0159] 1 Positive Electrode
[0160] 2 Negative Electrode
[0161] 3 Separator
* * * * *